# [LeetCode] Binary Tree Level Order Traversal II 二叉树层序遍历之二,LeetCode All in One 题目讲解汇总(持续更新中...)

Given a binary tree, return the bottom-up level order traversal of its nodes’ values. (ie, from left to right, level by level from leaf to root).

For example:
Given binary tree `{3,9,20,#,#,15,7}`,

```    3
/ \
9  20
/  \
15   7
```

return its bottom-up level order traversal as:

```[
[15,7],
[9,20],
[3]
]```

```class Solution {
public:
vector<vector<int> > levelOrderBottom(TreeNode* root) {
if (!root) return {};
vector<vector<int>> res;
queue<TreeNode*> q{{root}};
while (!q.empty()) {
vector<int> oneLevel;
for (int i = q.size(); i > 0; --i) {
TreeNode *t = q.front(); q.pop();
oneLevel.push_back(t->val);
if (t->left) q.push(t->left);
if (t->right) q.push(t->right);
}
res.insert(res.begin(), oneLevel);
}
return res;
}
};```

```class Solution {
public:
vector<vector<int>> levelOrderBottom(TreeNode* root) {
vector<vector<int>> res;
levelorder(root, 0, res);
return vector<vector<int>> (res.rbegin(), res.rend());
}
void levelorder(TreeNode* node, int level, vector<vector<int>>& res) {
if (!node) return;
if (res.size() == level) res.push_back({});
res[level].push_back(node->val);
if (node->left) levelorder(node->left, level + 1, res);
if (node->right) levelorder(node->right, level + 1, res);
}
};```

Average of Levels in Binary Tree

Binary Tree Zigzag Level Order Traversal

Binary Tree Level Order Traversal

https://leetcode.com/problems/binary-tree-level-order-traversal-ii/

https://leetcode.com/problems/binary-tree-level-order-traversal-ii/discuss/35089/Java-Solution.-Using-Queue

https://leetcode.com/problems/binary-tree-level-order-traversal-ii/discuss/34981/My-DFS-and-BFS-java-solution

LeetCode All in One 题目讲解汇总(持续更新中…)

原文作者：Grandyang
原文地址: https://www.cnblogs.com/grandyang/p/4051326.html
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